Mobile charge carrier traps present in a semiconductor device can affect the reliability of the device and cause yield losses in the manufacturing of such semiconductor devices. As such, mobile charge carrier trap defects can adversely impact the performance and manufacturing cost of semiconductor devices. For example, mobile charge carrier trap defects can cause aperiodic Random Telegraph Noise (RTN) to be present in the threshold voltages of the semiconductor device, thus altering the device's operating characteristics such as, for example, switching voltage or current thresholds.
Conventionally, RTN has been thought to be an elementary noise in 1/f (e.g., flicker) noise. If an active volume of a device is small enough to allow only one defect per semiconductor device, the noise has a binary waveform, the binary two states of which correspond to the two states of the single defect in the device. For example, FIGS. 1A and 1B illustrate the physical origin and statistical nature of RTN in a Metal Oxide Semiconduct Field Effect Transistor (MOSFET) device. As shown in FIGS. 1A and 1B, the capture and emission of an electron at a trap near a silicon-insulator interface results in bistable alternation (increase and decrease, respectively) of the threshold voltage (Vth) of the MOSFET.
When the active volume is further reduced, the probability of finding the defect in a device is correspondingly lowered. On the other hand, it is statistically inevitable that a given device will have two or more such trap defects.
In addition, a defective device shows extremely singular characteristics if the active volume is small enough for the change of states of the defects to significantly affect the operation of the device. As a result, the complex RTN case is widely accepted as a major cause of yield loss, especially in flash memory devices.
In view of the practical importance of detecting complex RTN defects, a robust procedure for analyzing and determining the complex RTN characteristics is desirable. Conventional techniques directed to quantitative extraction of the physical constants of RTN are limited in scope to simple, one-defect RTN. The effects of Gaussian noise on the measured signal can also cause difficulty in reliably distinguishing the presence of multi-trap defects.